Development of a Mn 2 O 3 ‐based Water Oxidation Electrocatalyst From a Naturally Occurring Bixbyite Ore

Abstract With the aim of achieving a sustainable society, it is crucial to develop catalysts for the oxygen evolution reaction (OER) to improve the efficiency of hydrogen production via water electrolysis. Manganese oxide catalysts containing Mn(III) species have been reported to exhibit high OER activity. Additionally, catalysts derived from natural minerals offer advantages in terms of cost‐effectiveness and resource sustainability. In this study, we developed an OER electrocatalyst by ball‐milling bixbyite (Mn 2 O 3 ), a naturally occurring manganese mineral. The catalyst exhibited an OER onset at 1.6 V versus RHE and maintained stable oxygen evolution for over 2 h. X‐ray absorption fine structure (XAFS) analysis was conducted on Mn and O sites in the catalyst, accompanied by detailed simulations based on full‐potential multiple scattering (FPMS) theory. Under water‐splitting conditions, the Mn K‐edge XAFS was found to shift to higher energy, suggesting that oxidation of Mn species occurs during the reaction and is associated with the formation of active OER sites. These findings highlight the potential of using Mn₂O₃ ores to develop efficient and sustainable OER electrocatalysts through a simple ball‐milling approach.